As many as 60 percent of existing Adélie penguin colonies in Antarctica undergo decline by 2099 as a result of climate change, according to a new study.
Penguins are commonly associated with the coldest places on Earth, but the Adélie is one of only two species that live and breed on the mainland of Antarctica and its fringing pack ice. The other is the emperor penguin, famed and beloved for starring in the Morgan Freeman-narrated documentary; several other species occupy the Antarctic Peninsula region and sub-Antarctic islands, while others live as far afield as New Zealand, South Africa and the Galapagos.
In a paper published Thursday in the journal Scientific Reports, a team of scientists led by Megan Cimino of the University of Delaware anticipates that changing climate will reduce available breeding habitat: the latest twist in an intertwined story of penguins, climatic changes and human impacts that at various times and in various parts of the continent has been to the species' benefit as well as its detriment.
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For example, the geologic record shows that at times in the past, a degree of warming has benefited Adélies: as glaciers expanded and covered the species' breeding habitats with ice, colonies were abandoned; when the glaciers melted during warming periods, the penguins were able to return to their rocky breeding grounds.
A 2014 study, using satellite imagery, found a total of 251 Adélie penguin colonies and estimated that the population numbered about 3.79 million -- an increase of 53 percent over the previous survey, conducted 20 years previously. But the increase was not uniform: Generally, the population was growing along a segment of coast from Terre Adélie -- named, like the penguin after Adéle Dumont d'Urville, wife of a French explorer -- to Victoria Land, and especially in the Ross Sea, an area that lies approximately south of New Zealand; on the western Antarctic Peninsula (south of South America), however, the population was declining, with eight colonies considered to have gone extinct.
The population growth in the Ross Sea region is likely due to a combination of factors, including declines in Patagonian toothfish, which compete with them for prey, and an expansion in sea ice; the decreases in the Peninsula, however, are notable, and the reason for them seems clear.
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"I have worked extensively at Palmer Station and we know that penguin colonies near there have declined by at least 80 percent since the 1970s," said Cimino in a press release. "Within this region we saw the most novel climate years compared to the rest of the continent. This means the most years with warmer than normal sea surface temperature. These two things seem to be happening in the Western Antarctic Peninsula at a higher rate than in other areas during the same time period."
Cimino and colleagues used satellite observations from 1981-2010 of sea surface temperature, sea ice and bare rock locations, as well as of the presence or absence of penguin populations; in particular, they examined the number of years during that period with novel or unusual climate during the Adélie penguin chick-rearing season. They then used an ensemble of global climate models to make predictions about Adélie penguin habitat suitability from 2011-2099.
They found a strong negative correlation between warm sea surface temperatures and Adelie breeding success -- a particular cause for concern in the Antarctic Peninsula region, which is among the fastest-warming places on Earth. It is in this area in particular that Cimino and colleagues predict the most severe colony declines.
The news is not entirely grim, however; whereas the Peninsula is predicted to continue experiencing extreme temperature increases, other parts of Antarctica are expected to warm to a lesser extent -- and these include some of those areas where Adelies have been doing comparatively well.
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"The Cape Adare region of the Ross Sea is home to the earliest known penguin occupation and has the largest known Adélie penguin rookery in the world," said Cimino. "Though the climate there is expected to warm a bit, it looks like it could be a (refuge( in the future." In such areas, where habitat is likely to be suitable past the end of the century, she added, "the penguins should be fine."
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